Use Redis cache for branch existence checks

Closes #40349

See merge request gitlab-org/gitlab-ce!15513

Update CONTRIBUTING.md: Link definition of done to criteria

See merge request gitlab-org/gitlab-ce!15500

FileUploader should use Hashed Storage only when project is migrated

See merge request gitlab-org/gitlab-ce!15526

Simplify Feature Proposal template

See merge request gitlab-org/gitlab-ce!15297

Use arrays in Ci::Pipeline#latest_builds_with_artifacts

See merge request gitlab-org/gitlab-ce!15525

Use `make install` for Gitaly setups in non-test environments

See merge request gitlab-org/gitlab-ce!15295

Fix blank states using old css

Closes #40377

See merge request gitlab-org/gitlab-ce!15521

Add wiki css to help page

See merge request gitlab-org/gitlab-ce!15488

This changes Ci::Pipeline#latest_builds_with_artifacts so it returns an
Array instead of a relation. Whenever we use this data we do so in two
steps:

1. Count the number of rows
2. If this number is greater than 0, iterate over the rows

By returning an Array instead we only execute 1 query of which the total
time/work is less than running either just a COUNT(*) or both queries
(in the worst case).

On GitLab.com this change should save us a few milliseconds per request
to ProjectsController#show.

Optimize read-only middleware so that it does not consume as much CPU

Closes #40185 and gitlab-com/infrastructure#3240

See merge request gitlab-org/gitlab-ce!15504

Skip confirmation user api

Closes #28934

See merge request gitlab-org/gitlab-ce!15175

Custom issue tracker

See merge request gitlab-org/gitlab-ce!15516

Resolve "Notes API for issues no longer returns label additions/removals"

Closes #39461

See merge request gitlab-org/gitlab-ce!15080

Resolve "TagsPage|Tags"

Closes #40367

See merge request gitlab-org/gitlab-ce!15512

This reverts commit 91075c82.

Batch load blobs for diff generation

Closes #37599

See merge request gitlab-org/gitlab-ce!15370

Fix promoting milestone updating all issuables without milestone

Closes #40337

See merge request gitlab-org/gitlab-ce!15487

After installing a new gem, batch-loader, a construct can be used to
queue data to be fetched in bulk. The gem was also introduced in both
gitlab-org/gitlab-ce!14680 and gitlab-org/gitlab-ce!14846, but those mrs
are not merged yet.

For the generation of diffs, both the old blob and the new blob need to
be loaded. This for every file in the diff, too. Now we collect all
these so we do 1 fetch. Three `.allow_n_plus_1_calls` have been removed,
which I expect to be valid, but this needs to be confirmed by a full CI
run.

Possibly closes:
- https://gitlab.com/gitlab-org/gitlab-ce/issues/37445
- https://gitlab.com/gitlab-org/gitlab-ce/issues/37599
- https://gitlab.com/gitlab-org/gitlab-ce/issues/37431

since `Rails.application.routes.url_helpers` creates a new anonymous module every time it's called

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Fix slow gitaly dev test bundle

See merge request gitlab-org/gitlab-ce!15508

Signed-off-by: Rémy Coutable <remy@rymai.me>

Export code as ES6 modules

See merge request gitlab-org/gitlab-ce!15503

Backport ability to enable/disable file attachments in issuable form

See merge request gitlab-org/gitlab-ce!15433

Memoize GitlabShellAdapter for performance and ease of testing

See merge request gitlab-org/gitlab-ce!15507

Fix commits list 500 with multi-file editor new_repo cookie

Closes #39821

See merge request gitlab-org/gitlab-ce!15502

Remove a useless `allow_failure: no` and use `true` instead of `yes`

See merge request gitlab-org/gitlab-ce!15491

Port of https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/3463#note_47990536